Male flamingos produce and use their own make-up pigments to colour their feathers before displaying to potential mates, a new study shows.

They get their 'make-up' from the uropygium glands, the area from which their tail feathers grow.

In a paper published in Behavioral Ecology and Sociobiology, a team of Spanish researchers has confirmed what had long been suspected - there are red and yellow carotenoid pigments in a flamingo's preening oils. The authors believe this is the first time it has actually been demonstrated and documented.

Juan Amat, of the Department of Wetland Ecology, Estación Biológica de Doñana, in Seville, Spain, and his colleagues, studied the greater flamingo, Phoenicopterus roseus, and believe that the pigments are used as signal amplifiers.

The research team recorded the plumage maintenance behaviour by flamingos in Southern Spain, during periods of group display (in the lead up to mate selection) between October and April. They compared these observations to the May to September period when no group displays were observed.

The team collected uropygial secretions and feathers from a sample of captive birds taken from the population under observation and then subjected the samples to high performance liquid chromatography (HPPLC).

These revealed that during display periods, the flamingos were actually secreting more of the pigments, which bolstered their theory that the birds were deliberately enhancing their colours.

Showing off their condition

Dr Sarah Pryke from the Biology Department at Macquarie University in Sydney, says the phenomenon is quite rare.

"There are some suggestions that vultures for example coat themselves with red dust and that it might be used for display purposes, but as far as I know there isn't really much evidence for this kind of thing in birds", Dr Pryke says.

Carotenoids are the basis of colours such as red, yellow and orange. These colours are incorporated into feathers during moult, but the animals can't actually synthesise the pigments, and they have to be ingested with food. Therefore the more colourful plumage may signal a better ability to locate resources.

"What they're also saying is, I am able to spend my time displaying to a female, because I'm in good enough condition. Obviously males who are in better condition are better able to forage. So they have the time and resources to invest that into display."

Interestingly, the birds with the most colourful plumage also did the most cosmetic preening.

Traditionally plumage colour has been considered a static trait which individuals have little chance to alter.

"Most birds have these oil glands," Pryke says, "especially water birds: It's the way they waterproof themselves. It's just that nobody has ever actually looked at the pigments inside those glands, and that for me is the great thing about this research.

"We've always just thought of it as a functional mechanism to waterproof their feathers, as opposed to whether they're signalling as well. It will be interesting to see now if other birds are doing the same thing.

So the birds which spend more time looking pretty are more attractive to mates, and because they nest sooner they end up with the best nesting sites.

Interestingly, Juan Amat and colleagues observed that the birds usually allowed their plumage to fade soon after the pair started to breed.